Fail-safe sensor/override for circuit

ABSTRACT

A temperature override sensor for a control circuit for a heating device including an electric switch and temperature control means to control and regulate the amount of heat developed by a heating device. The temperature override sensor is so connected in the circuit as to be operable to permit normal temperature control operation of activators for the heating element in a desirable ambient temperature condition, and operable under abnormal blanket and ambient temperature conditions to override the normal operating components and circuitry to shut off completely functioning of the heating element or device. This is accomplished by physically mounting the temperature override sensor on a control or operating actuator for the heating element or device, so that a critical sensing of the temperature of the actuating device is compared with the, for example, voltage divider in receptacle and with the temperature range in which the heating device is utilized, the disparity between the two temperature ranges in the voltage divider means, one critical, one wide, permits the use of the safety override device that will cut off any control, and which further does not interfere with the normal operation of the heating control itself unless an untoward or unsafe condition of room temperature or connection plug temperature exists.

United States Patent [72] Inventor PeterLauck,Ill

Princeton, NJ. [21] Appl. No. 866,355

[22] Filed Oct. 14,1969

Continuation-impart of application Ser. N 0. 810,156, Mar. 25,1969 {45] Patented Feb. 16, 1971 [73] Assignee J.P.Stevens& Co., Inc.

New York, N .Y.

[54] FAIL-SAFE SENSOR/OVERRIDE FOR ZIRCUIT 5 Claims, 2 Drawing Figs. 52 U.S.Cl. 219/501, 219/505 [51] Int.Cl....'. H05b 1/02 [501' FleldolSearch 219/497, I

[56] References Cited UNITED STATES PATENT 3,303,391 2/1967 Kitami..... 307/310 3,465,175 9/1969 Sutton....

Primary Examiner-Bernard A. Gilheany Assistant ExaminerF. E. Bell Attorney-J. Gibson Semmes ABSTRACT: A temperature override sensor for a control circuit for a heating device including an electric switch and temperature control means to control and regulate the amount of heat developed by a heating device. The temperature override sensor'is so connected in the circuit as to be operable to permit normal temperature control operation of activators for the heating element in a desirable ambient temperature condition, and operable under abnormal blanket and ambient temperature conditions to override the normal operating components and circuitry to shut off completely functioning of the heating element or device. This is accomplished by physically mounting the temperature override sensor on a control or operating actuator for the heating element or device, so that a critical sensing of the temperature of the actuating device is compared with the, for example, voltage divider in receptacle and with the temperature range in which the heating device is utilized, the disparity between the two temperature ranges in the voltage divider means, one critical, one wide, permits the use of the safety override device that will cut off any control, and which further does not interfere with the normal operation of the heating control itself unless an untoward or unsafe condition of room temperature or connection plug temperature exists.

70K D/AC BACKGROUND OFTHE INVENTION l.Fieldofthe.Invention .The invention has particular .use in applications utilizing heating devices in which activation of the heating element is controlled by a circuit including-means acting as a temperaturesensor and control activator for the'heating device. The

invention has particular .use in applications such as electric blankets, or.other electrically heated'fabrics or materials such aswoven or nonwoven drapes, floorcoverings and the like for V better additional and differentconsumerprotection thanthat .presently provided. (bimetallic-means in blanket area) 2. Description of theiPrior Art Theprior art discloses utilization of 'heatingndeviees in, for example, flexible blankets and sheet heatingdevices, in which actuationof the heating elementis controlled by temperature control sensorsor actuators such as bimetallicswitches, thermostats, silicon controlled rectifier (SCR) circuits, thyristor circuits andthe'like. Related inventions disclosing circuitry-to which the present invention is applicableincludeLP. Lauck, III U.S.Pat. No. 3,385,958 issued May 28, 1968 entitled Electric Blanket; U.S. Pat. No. 3,422,244 issued Jan. 14,1969 entitled Electric Blanket with a TemperaturejResponsive Control Circuit; U.S. Pat. No. 3,437,792, issuedApr. 8, 1969 entitled Electric Heating Device with Temperature Control Means; application Ser. No. 8l0,l56, filed Mar. 25, =l969 entitled Heating Control Circuit with Triac-Diac'Combination; and

application Ser. No. 810,948, filed Mar. 27, I969 entitled Heating Control Circuit with Combination.

Such control circuitry in the prior art accordingly are comprised essentially of Lauck" temperature control circuits with various selective actuating'means for a heating element and the use of sensors regulating sleeping area temperature. The present circuit incorporates a temperature override sensor which preferably is physically placed against a thyristor, SCR or triac, or other device or devices which senses their temperature when they are turned on, and which, when connected in the Lauck" or other circuits, regulates the supply voltage to the heating element to cut it off to a preset tempera- SCR-Unijunction Transistor ture of the actuating device as a function of the disparity of temperature range of operation of the heating device and temperature in the heating element actuator or receptacle itself.

This constitutes a safety override device operable under certain operating conditions to permit normal operation of the heating element or provides a complete breaking of the circuit within the control element itself, and complements existing electronics of known sensing and control devices. Additionally, the present invention incorporates utilizationof a v heat sink for heat dissipation from actuating devices, such for example, as a thyristor or combinations thereof or equivalents.

SUMMARY OF THE INVENTION" The present invention accordingly is directed to a temperature override sensor which serves as a circuit cutoff device which is physically mounted on thecase of a heating actuator in a desired control area permitting regulation of heat to a critical degree, and operable upon agiven rise in temperature to automatically cut off the circuit operation without impeding normalprogress of temperature, even in high settings in a I applications but without affecting usual temperature control.

The override circuit can constitute a thermostatic mechanism serving as a heat sink in addition to its safety override featu res,

or can comprise an electronic override but in either case the mounting would be physically on the case of an SCR thyristor or other equivalent heating device actuating mechanism.

BRIEF DESCRIPTION OF THEDRAWINGS FIG. 1 depicts circuitry in accordance-with the invention incorporating a thyristor actuator for a heating element;

FIG. 2 depicts circuitry in accordance with the invention incorporating an SCRheating element actuator. 1

It is to be understood thatthe'FlGS. of the drawings disclose illustrative embodiments of circuits only, and the invention is in no way to be restricted thereto, since it is susceptible of broader application to different specific control circuits as referred to above,'in patented and'pending patent application embodiments, or others.

ventional alternating current supply applied between input. terminals 1 and 2. The series connection of H heating device 'or heater coil L, resistor R1, Temperature Sensor T, resistor R2 is interconnected to terminals 1 and 2. Additionally, the series connection of heat control actuator shown as a triac TR, but which can be any suitable thyristor, or equivalent and switch SW, utilizing the main terminals of triac TR, is also interconnected to terminals 1 and 2. The sensor can, for example, consist of a thermistor, the term "temperature sensor" by definition is a device which evaluates the temperature and balances and regulates electronicsi in a circuit. It can have either a positive or negative temperature coefficient, which, depending upon use in conjunction with other variable resistors and/or capacitors, will serve to critically effect triggering or timing of a thyristor or SCR circuit. The foregoing is described in detail in my aforementioned patents and applications for patents. V

A temperature override sensor TOR is connected in series with a diac and potentiometer or variable resistor R3 between the gate of Triac (thyristor) TR and the series connection of Temperature Sensor T and resistors RI and R2. The temperature override sensor TOR can consist of a thermostat such as a bimetallic member, but can include either an electrical/mechanical device or a solid state thermistor device and the like. TOR can be referred to as a thyristor heat sink thermostat when used in the circuit of FIG. 1, and is physically placed on and associated with the case of thyristor TR and thereby senses directly the temperature of the case. Sensor T and the relative values of circuit components including resistor R2, sensor T, and resistor Rl, are chosen to control the duty cycle of thyristor TR, depending upon the selected temperature which the heating device is set by potentiometer or variable resistor R3. v

The sensor T is preferably placed in an area in which temperature is desired to be controlled, such as a blanket or zone or region thereof, and the actual control is effected by the area controlled by the heating device which affects the temperature of sensor T. Upon energization of the circuit, and upon the heat value or temperature sensed by sensor T being lower than the desired temperature as regulatable by variable resistance R3, thyristor TR will be energized to thereby activate heater coil L. The converse is true upon the temperature rising above a predetermined desired value, whereupon, as sensed by sensor T, the triac (thyristor) TR will discontinue conductance. In essence, thyristor or triac TR comprises a gate circuit which activates heating device L when it is conducting, and deactivates heating device L when it is not conducting. The amount of heat developed by heating device L is dependent upon length of operation of the duty cycle of thyristor or triac TR. Resistor R1 is provided to limit power control. ln thisembodiment, the thyristor heat sink thermostatTOR (triac,

SCR or equivalent) is physically placed on thyristor TR, but

ment such as when used in a blanket. The sensor TOR in other words,;controls the off/on state of the thyristor TR independently of the sensor or thermistor T control function. By

mounting the sensor TOR physically on top of the case of, for

example, a solid state thyristor, it is possible to regulate heat to a critical degree and therefore, once it turns on it can rise to, for example, approximately 95 F., and then automatically cut off all the rest of the electronics inthe circuit without impeding the nonnal action of the thermistors in the blanket, for example, which will operate on the normal mode in a cold room under normal conditions. In an abnormal condition, in a warm room, the sensor TOR which also .canserve as a heat sink device for the thyristor TR, would rise to, for example, 95 F. and shut off all the circuitry to prevent damaging conditions. In essence, the invention is directed to disparity of temperature range for a given area to be controlled (including the voltage divider components) and the physically mounted temperature sensor on the, thyristor, case in receptacle. Since every thyristor dissipates heat and sometimes needs the addition of'a heat sink for this dissipation, the present invention serves the function of not only"dissipating the heat as a heat sink, but also critically senses the temperature of the thyristor case. The temperature range'of the area heated by the heating element and the safety override device as applied directly to medium (resistive voltage divider) being wide and as applied to the thyristor'case being critical, permits the use of the safety override device which can act to cut off any control, and will not interfere with the normal solid state electronics of the control with its sensing means located in another area itself unless an untoward or unsafe condition of room temperature. or circuit actuating plug temperature is involved.

With reference to-FlG. 2, it will be noted that the circuit as applied to terminals 1 and 2 includes in series, Heater l-l, heater element L,diode D, resistance R1 and temperature sensor T (thermistor) connected with the terminals. A thyristor, as shown, silicon controlled rectifier SCR is also connected operatively with terminals 1 and 2.in parallel to the first mentioned'series circuit together with Switch SW and Fuse F in an SCR series connection. Temperature override sensor TOR, in the nature of a thermostat or thermistor having the desired heat operating characteristics, is connected in series with potentiometer or variable resistance R2 and resistor R3 between thegate of silicon controlled rectifier SCR and the series connected between resistance R1 and sensor T. The

temperature override sensor TOR again is physically mounted on the case of thyristor or silicon controlled rectifier SCR and serves as a heat sink to the thyristor forheat dissipation when .in the on state, but electrically opens or closes the gate trigger with reference to SCR current to provide a mechanical failsafe control in balance with the solid state electronics for temperature regulation and switching. lt does not affect normal control of heating element L under allowable desired surrounding temperatures, but when present in undesirably high temperatures and upon affected critical rise in temperature of SCR serves as a heat sinkoverride control triggering fail-safe mechanism for the thyristor. The values of the various components utilized in the circuit will,-of course, govern actuation the case of the thyristor, one'range is applied to the heated which would break the-voltage down from, for example, ll0 volt AC to a reference voltage desired, in order to amplify or eventually trigger the-SCR or thyristor. In such an arrangement a unique situation might exist in that such a voltage divider ranges in temperature from approximately 120 F. down to approximately 80 F., or at worst 85 F., depending upon whether or not the thyristor itself isfiring'. in other words. in an off state, the voltage divider temperature in a plug connector might be in the area of 120 F.,however, whenthe SCR or thyristor fires, the voltage divider temperature drops to about 85 F., but the case of the thyristor rises to'approximately 95 F. By mounting the TOR device physically on top of the case of a solid state thyristor, it is possible to regulate heat to a critical degree and therefore once it turns on, it can rise to about 95 F. and then automatically cutoff all the restof the electronics-in the circuit without impeding the normal progress of thermistors or the like in a blanket or the like, which will operate on the normal mode in a cold room under normal conditions. In an abnormal condition, as in a warm room, this heat sink device would rise to 95 F., approximately, and shut off all the circuitry. The TOR device can be incorporat'edin four different positions electrically while physically it is mounted on the thyristor case. The four positions are as follows:

1. in the gate of the thyristor trigger mechanism; 2. in a reference voltage position between the anode of the thyristor, and the anode of a rectifying diode just prior to perature of the case thereof, and at least a 20 spread on the voltage divider itself. For example, in an off state of the SCR the voltage divider temperatureis about 120 F. in the plug. Once the SCR fires the temperature of its case rises, andthe voltage divider resistors decrease their temperature. They do so in a disproportionate degree. which is sufficiently radical that it enables the mechanism not to interfere with the normal electronics. Again, accordingly, the essence of the invention resides in utilization of the disparity'of the temperature range between the voltage divider itself and the physically mounted temperature sensoronthe thyristor case to provide fail-safe control overand above permitted normal operation of the .heating element through the temperature sensors associated with an area or region wherein the temperature is to be controlled. It will be understood that the override circuit can be in the nature of a thermostatic mechanism serving as a heat sink in addition to its safety override features, or can consist of an electronic override. In any event, the mounting would be physically on the eased the SCR and/or thyristor, for thermal conductivity but insulated from it, andelectrically connected so electrically incorporated in the circuit as to control normal and additionally undesirable operating conditions. The location of the sensor can be in a control area feasibly positioned.

. Manifestly, minorchangesin details of construction and arrangement of parts and circuitry, within the teachings of the present invention, can be affected without departing from the spirit and scope of the invention as defined in and limited solely by the appended claims. P

I claim: a

1. In an electrical heating system and control circuit therefor including a heating element, voltage divider means, a temperature sensor and a heating element actuator, controllable by and in accordance with temperatures sensed by the sensor to operatively energize and deenergize the heating element, the improvement comprising:

A. a temperature override sensor physically associated with said actuator and electrically connected in said circuit substantially between said voltage dividermeans and the actuator;

B. said voltage divider means including resistors operable to break input voltage to a reference voltage adapted to amplify or trigger said actuator, the voltage divider means affording a wide temperature range during operation thereof; and

C. said temperature override sensor being such, when so associated and circuit connected, as to operate to directly a thyristor, or combinations thereof.

3. The invention of claim 1 wherein said actuator comprises a silicon controlled rectifier, or combinations thereof.

4. The invention of claim 1, wherein the circuit is an integrated circuit.

5 The invention as claimed in claim 4, wherein said temperature override sensor comprises a thermistor. 

1. In an electrical heating system and control circuit therefor including a heating element, voltage divider means, a temperature sensor and a heating element actuator, controllable by and in accordance with temperatures sensed by the sensor to operatively energize and deenergize the heating element, the improvement comprising: A. a temperature override sensor physically associated with said actuator and electrically connected in said circuit substantially between said voltage divider means and the actuator; B. said voltage divider means including resistors operable to break input voltage to a reference voltage adapted to amplify or trigger said actuator, the voltage divider means affording a wide temperature range during operation thereof; and C. said temperature override sensor being such, when so associated and circuit connected, as to operate to directly sense temperature of said actuator by differentiation therebetween and a given area temperature extraneous thereto, including the voltage divider means, to thus control open or closed circuit conditions, independent of normal control and operation of said heating element by said temperature sensor as a fail-safe override safety temperature control.
 2. The invention of claim 1 wherein said actuator comprises a thyristor, or combinations thereof.
 3. The invention of claim 1 wherein said actuator comprises a silicon controlled rectifier, or combinations thereof.
 4. The invention of claim 1, wherein the circuit is an integrated circuit.
 5. The invention as claimed in claim 4, wherein said temperature override sensor comprises a thermistor. 